also genetics mate...one of my RTCs are REALLY dark in pigmentation...even the tail is a deep reddish colour. however the other RTC is much lighter and the tail is a brighter and lighter red than the other. they eat the exact same thing as well!necrocanis;2715702;2715702 said:Tail color comes with time more than diet. It starts as a brownish black and turns red around the 8"-14" mark. Some are slower than others. I've always fed mine shrimp, and fish fillets, and the tail is striking at 28-30".